Switch mode power supplies or switching regulators, also referred to as DC to DC converters, are used to convert an input supply voltage to a desired output voltage at a voltage level appropriate for integrated circuits in an electronic system. For example, a 12 volts supply voltage provided to an electronic system may need to be reduced to 5 volts for supplying the I/O interface circuits and reduced to 1 V for supplying the core digital logic circuits. A switching regulator provides power supply function through low loss components such as capacitors, inductors, and transformers, and power switches that are turned on and off to transfer energy from the input to the output in discrete packets. A feedback control circuit is used to regulate the energy transfer to maintain a constant output voltage within the desired load limits of the circuit.
The operation of the conventional switching regulator is well known and is generalized as follows. A switching regulator includes a pair of power switches which are turned on and off to regulate an output voltage in relation to a reference voltage. More specifically, the power switches are alternately turned on and off to generate a switching output voltage at a switching output node, also referred to as the switch node. The switch node is coupled to an LC filter circuit including an output inductor and an output capacitor to generate an output voltage having substantially constant magnitude. The output voltage can then be used to drive a load. Switching regulators include a control circuit which typically uses an error amplifier to compare a feedback voltage indicative of the output voltage with a reference voltage and the control circuit generates one or more control signals that control the switching frequency (pulse frequency modulation) or the pulse width (pulse width modulation) of the on-off switching cycle. Many different control schemes have been applied to control the duty cycle (i.e., the on-time) of the power switches.
Multi-phase switching regulators and multi-phase converters are known in the art. A multi-phase converter consists of paralleled power stages which drive a common load. The switching signals for each of the power stages are out of phase with each other. For example, one power stage might be opening a switch while another is closing a switch. Each power stage continues to operate on the same clock frequency. A multi-phase controller is typically used to control the multiple power stages in multi-phase operation. Multi-phase switching regulators realize many benefits including higher efficiency, faster transient response and higher current capability.
FIG. 1 is a schematic diagram of a conventional multi-phase switching regulator. Referring to FIG. 1, a multi-phase switching regulator 10 includes a multi-phase controller 12 driving N parallel power stages 22. Each power stage 22 is coupled to a respective output inductor L1 to LN. The output nodes of the output inductors L1 to LN are coupled to an output capacitor Cout to form the LC filter circuit to generate the regulated output voltage Vout (node 24) having a substantially constant magnitude. The output voltage Vout can then be used to drive a load 30 whereby switching regulator 10 provides the load current Load to maintain the output voltage Vout at a constant level. In some examples, the power stage 22 is implemented as a pair of power switches connected in series between an input voltage Vin and ground. The power switches can be N-type MOSFET devices or P-type and N-type MOSFET devices.
The multi-phase controller 12 implements feedback control of the power stages 22 to regulate the energy transfer to the LC filter circuit to maintain a constant output voltage within the desired load limits of the circuit. In particular, the multi-phase controller 12 receives a feedback voltage Vfb on a feedback node 26. The feedback voltage Vfb can be the regulated output voltage Vout or a divided down voltage of the regulated output voltage Vout. The multi-phase controller 12 generates the control signals, such as pulse-width-modulation (PWM) control signals PWM1 to PWMN, to cause the power switches in each power stage to turn on and off to regulate the output voltage Vout in relation to a reference voltage Vref. For example, the multi-phase controller 12 can include an error amplifier, a proportional-integral-derivative (PID) calculator, and a digital pulse-width-modulation (PWM) generator to generate the PWM control signals (node 19) for driving the respective power stage 22. Multi-phase controller 12 includes a memory 20 storing pre-set configuration parameters used in controlling the operation point of the switching regulator and the feedback control of the power stages 22.
Furthermore, the multi-phase controller 12 operates to select the number of phases, or the number of power stages, to activate in response to the load current demand. For example, the multi-phase controller 12 may implement dynamic phase management whereby a selected number of phases, or power stages, is activated based on the load current demand and using pre-set phase current thresholds. To that end, the controller 12 receives a sense current Isens (node 27) indicative of the load current ILoad supplied to the load 30. The pre-set phase current thresholds and other configuration parameters for the feedback control operation may be stored in the memory 20. In some examples, the multi-phase controller 12 may be configured to control 5, 6 or 8 power stages. Each power stage has an associated maximum current limit (e.g. 60 A) being the maximum current that can be handled by the output inductor associated with the power stage. The controller activates a given number of power stages to distribute the load current demand over one or more power stages so that each power stage operates within its own current limit. Under conventional dynamic phase management schemes, the multi-phase controller 12 is configured with a set of pre-set phase current thresholds for selecting different combination of phases in response to the load current demand. For example, for load current values lower than a first phase current threshold, the controller 12 activates one power stage; for load current values equal to or greater than the first phase current threshold but lower than a second phase current threshold, the controller 12 activates two power stages, and so on.
In one example, assuming each power stage 22 in switching regulator 10 has a maximum current limit of 60 A. The controller 12 is configured with pre-set phase current thresholds of up to 40 A for one power stage, up to 80 A for two power stages and up to 120 A for three power stages, and so on. During operation, when the load current demand is less than 40 A, only one power stage is activated. When the load current demand increases to or exceeds 40 A, the first phase current threshold is reached and two power stages are activated. In the case the load current demand increases to 80 A or higher, the second phase current threshold is reached and three power stages are activated. In this manner, the controller 12 selectively turns on different number of power stages based on load current demand.